The present invention relates to the process for the preparation of 3-chloromethylarylcyclobutene compounds.
In recent years, the search for high-performance materials, especially high temperature-resistant polymers, has gained momentum. In order for polymeric materials to have stability at high temperatures, they must fulfill several requirements, including high melting or softening temperatures, high modulus or rigidity, a resistance to solvent and chemical degradation and toughness. The intrinsic thermal and oxidative stability of aromatic structures has long been recognized, and a variety of polymers have been made in which benzene rings ar linked together by various connecting groups.
Aromatic hydrocarbons which have cyclobutene rings fused to the aromatic nucleus are useful in the preparation of high-performance polymers. These high-performance polymers exhibit thermal stability at elevated temperatures, chemical resistance to most conventional solvents, good mechanical and electrical properties, and low sensitivity to water. They are useful as films, advanced composites, adhesives, structural laminates, matrix resins, and planarization resins for the electronics and aerospace industries.
The cyclobutene-substituted aromatic hydrocarbons are also suitable for preparing aromatic ring-substituted intermediates which are themselves polymerizable or can be used to introduce the arylcyclobutene moiety into a variety of monomers and polymers to enhance heat resistance of the ultimate products. It is, however, quite difficult to introduce reactive groups into the aromatic nucleus of arylcyclobutene compounds because severe reaction conditions which are often required for such nuclear substitutions can result in an undesired opening of the cyclobutene ring. In addition, yields of the desired product are often too low for commercial acceptability.
Haloalkylated derivatives, particularly halomethylated derivatives, of aromatic organic compounds are a particularly desirable intermediate because the chloromethyl or bromomethyl group can be easily converted to other groups such as --COOH, --CH.sub.2 OH, --CHO, --CH.sub.2 CN and --CH.sub.3. The chloromethylation of aromatic compounds is a well-known reaction. The chloromethylation of aromatic compounds involves the replacement of a hydrogen atom on the cyclic nucleus of an aromatic ring by a chloromethyl group in a single operation. The reaction typically proceeds at temperatures in the rang from 0.degree. to 120.degree. C. under acidic conditions. Thus, aromatic and alkaryl hydrocarbons have been chloromethylated by treatment with formaldehyde and hydrochloric acid; paraformaldehyde, zinc chloride, and hydrogen chloride; or paraformaldehyde, concentrated sulfuric acid, and hydrogen chloride.
Other effective chloromethylating reagents include .EPSILON.,.EPSILON.'-bischloromethyl ether and monochloromethyl methyl ether. The reaction is typically carried out in the presence of zinc chloride, stannous chloride, stannic chloride, aluminum trichloride, boron trifluoride, ferric chloride, titanium tetrachloride, as well as protic acids such as hydrogen chloride (taken in excess and behaving simultaneously as a reactant), sulfuric acid, phosphoric acid, chlorosulfonic acid and acetic acid. Zinc chloride is used most frequently, generally with a small amount of aluminum chloride to increase its activity. For example, 2,4,6-triisopropylbenzyl chloride is prepared by reacting chloromethyl ether with 1,3,5-triisopropylbenzene in the presence of stannic chloride at 0.degree. C.
Gilpin et al U.S. Pat. No. 4,562,280 disclose the chloromethylation of deactivated aromatic compounds which comprises contacting an aromatic compound substituted with an alkyl group and a deactivating group with a chloromethyl alkyl ether in an inert organic reaction medium in the presence of a catalytic amount of ferric chloride or stannic substituted with an alkyl group, a chloromethyl group and a deactivating group, wherein the alkyl and chloromethyl groups are on adjacent carbon atoms, is prepared. Generally, the Gilpin et al process is run at temperatures between about 40.degree. C. and 80.degree. C.
Attempts to chloromethylate arylcyclobutene compound at the known prior art conditions have been relatively unsuccessful because of the tendency of the cyclobutene ring which is fused to the aromatic nucleus to open under acidic conditions even at relatively mild temperatures, resulting in little, if any, yield of the desired chloromethylarylcyclobutene product. 4-chloromethylbenzocyclobutene has been prepared by the pyrolysis of 2,4-bis(chloromethyl)toluene in the gas phase at 700.degree. C., Ewing et al "Novel Syntheses of [2.2.2] (1,2,4) Cyclophane", J.C.S. Chem. Comm., 1979, pages 207-208.